Filling material is a term used to describe substances that are used to fill in gaps or cavities. GOLD and AMALGAM are two materials commonly used as filling material. GOLD, with four letters, is a precious metal that is malleable and ductile, making it an ideal choice for filling material. AMALGAM, with seven letters, is an alloy of mercury and other metals, such as silver, tin, and copper, which is also used as a filling material.